Author ORCID Identifier

https://orcid.org/0009-0000-9246-3464

Semester

Spring

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Joonhee Lee

Committee Member

Mikel Holcomb

Committee Member

Aldo Romero

Committee Member

Chunfei Li

Abstract

Neural electrode technology has been around for centuries since the times of Galvani. In early electrophysiology experiments metal wires were used to induce contractions in dissected animals. The metal wire electrode has since been a standard tool to both stimulate and record neural activity. In the past two decades, a new strategy for neural stimulation has been formulated based on the emergent field of optogenetics. Optogenetics refers to the use of light-sensitive proteins genetically imbedded in the membrane of a neuron to elicit neural activity. This technique offers more selectivity in the stimulation of neurons. Typical optogenetic neural electrodes, or optrodes, are composed of silicon which requires the integration of optical components such as optical fiber or waveguides. Using a transparent and conductive substrate removes the need for these additional components with their corresponding fabrication steps. The optical medium and the recording electrode are contained in one monolithic shank. One common challenge for transparent electrodes is light-induced noise during simultaneous recording and stimulation due to the photoelectric effect or the photoelectrochemical (Becquerel) effect. Here, an electrode device is proposed that has been fabricated on single crystal β-Ga2O3. It is shown that the device performs well to record artificial neural spikes in phosphate buffered saline. The device also displays excellent transparency in the visible range and no detectable photoelectric artifact.

A challenge presents itself in the fabrication of the device. Typical microfabrication techniques are optimized for 2D device structures. Neural probes require 3D considerations. For example, they must be hermetically sealed, requiring conformal coating of insulation. Traditional etching techniques are limited in their ability to open an electrode area through parylene-C, requiring a planar configuration of the electrode areas. Alternative approaches are needed for 3D configurations. In this dissertation, a new method for parylene etching is proposed. It was shown that selective laser ablation of the parylene layer of a parylene-coated gallium oxide device is possible with minimal damage to the underlying gallium oxide surface by using a sufficiently attenuated green (532 nm) picosecond pulsed laser. Further it was shown that this did not compromise the electrical properties of the gallium oxide surface which possessed a 1 kHz impedance magnitude under the acceptable maximum of 1 MΩ.

Download

Share

COinS